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POHow can I call a set of variadic base class constructors based on tagged argument packs?
 

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  1. POHow can I call a set of variadic base class constructors based on tagged argument packs?
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    <p>I'd like to be able to do this:</p> <pre><code>template&lt;typename Mix&gt; struct A { A(int i) { } }; template&lt;typename Mix&gt; struct B { B() { } B(const char*) { } }; template&lt;template&lt;typename&gt; class... Mixins&gt; struct Mix : Mixins&lt;Mix&lt;Mixins...&gt;&gt;... { // This works, but forces constructors to take tuples template&lt;typename... Packs&gt; Mix(Packs... packs) : Packs::Type(packs.constructorArgs)... { } }; template&lt;template&lt;typename&gt; class MixinType, typename... Args&gt; struct ArgPack { typedef MixinType Type; // pretend this is actually a template alias tuple&lt;Args...&gt; constructorArgs; ArgPack(Args... args) : constructorArgs(args...) { } } template&lt;typename... Args&gt; ArgPack&lt;A, Args...&gt; A_(Args... args) { return ArgPack&lt;A, Args...&gt;(args...); } template&lt;typename... Args&gt; ArgPack&lt;B, Args...&gt; B_(Args... args) { return ArgPack&lt;B, Args...&gt;(args...); } Mix&lt;A, B&gt; m(); // error, A has no default constructor Mix&lt;A, B&gt; n(A_(1)); // A(int), B() Mix&lt;A, B&gt; n(A_(1), B_("hello"); // A(int), B(const char*) </code></pre> <p>How do I fill in /* mysterious code here */ to do what I want, to provide a nice interface for calling some set of constructors of mixins? I have a solution that works by making all non-null constructs actually take a tuple of args, and then overloading figures out which one to call, but I would like to avoid constraining mixin authors by making them write a constructor A(tuple), instead of just A(int, int).</p> <p>Thanks!</p>
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    1. USCasey Rodarmor
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    1. COThe problem with your examples is that you keep using single-element tuples, so it's hard to know what behavior exactly you're after. If your goal is to expand a tuple into separate constructor arguments for `Base`, I don't think that's possible. Why not take a variadic parameter pack instead of a tuple as a constructor argument?
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      1. USildjarn
    2. COUgh, yeah, you are of course right. I'll put some thought into it and revise the question with an example that reflects my actual intent.
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      1. USCasey Rodarmor
    3. COCode now 100% more disgusting :)
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      1. USCasey Rodarmor
 

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